[[Geologists]] have deduced that petroleum is the remains of huge amounts of algal material that was laid down millions of years ago, and altered in form under high temperatures and pressures. Layers of buried plant material tend to produce [[coal]] or lignite. | [[Geologists]] have deduced that petroleum is the remains of huge amounts of algal material that was laid down millions of years ago, and altered in form under high temperatures and pressures. Layers of buried plant material tend to produce [[coal]] or lignite. |